Enhancement of Ultrahigh Rate Chargeability by Interfacial Nanodot BaTiO<sub>3</sub> Treatment on LiCoO<sub>2</sub> Cathode Thin Film Batteries

Nanodot BaTiO<sub>3</sub> supported LiCoO<sub>2</sub> cathode thin films can dramatically improve high-rate chargeability and cyclability. The prepared BaTiO<sub>3</sub> nanodot is <3 nm in height and 35 nm in diameter, and its coverage is <5%. Supported by high dielectric constant materials on the surface of cathode materials, Li ion (Li<sup>+</sup>) can intercalate through robust Li paths around the triple-phase interface consisting of the dielectric, cathode, and electrolyte. The current concentration around the triple-phase interface is observed by the finite element method and is in good agreement with the experimental data. The interfacial resistance between the cathode and electrolyte with nanodot BaTiO<sub>3</sub> is smaller than that without nanodot BaTiO<sub>3</sub>. The decomposition of the organic solvent electrolyte can prevent the fabrication of a solid electrolyte interface around the triple-phase interface. Li<sup>+</sup> paths may be created at non solid electrolyte interface covered regions by the strong current concentration originating from high dielectric constant materials on the cathode. Robust Li<sup>+</sup> paths lead to excellent chargeability and cyclability.